Synthesis, crystal structure and Hirshfeld surface analysis of N-(4-fluorophenyl)-N-isopropyl-2-(methylsulfonyl)acetamide

In the title compound, which is related to the herbicide flufenacet, the amide group and fluorobenzene ring are almost perpendicular. A short O⋯π contact is observed in the crystal.


Figure 2
A partial packing plot of I, showing inversion dimers resulting from pairs of C-HÁ Á ÁO weak hydrogen bonds, augmented by OÁ Á ÁCg(ring) contacts. Hydrogen atoms not involved in the hydrogen bonds are omitted.

Figure 1
The molecular structure of I showing 50% displacement ellipsoids.
tion of the benzene ring, and replacing one hydrogen of the methyl group, yielded 259 hits. A similar fragment, but with 'any halogen' at the 4-position on the ring, gave 92 hits. With the halogen restricted to fluorine, twelve hits were returned, and with an isopropyl group attached to the nitrogen atom, only one match was found: CSD refcode QEMHOG (Gao & Ng, 2006): this structure has a 1,3-benzothiazol-2-yl-oxy group attached to the methylene carbon atom of the search fragment. A search of the CSD for non-bonded close contacts (up to 3.1Å ) between S O oxygen atoms and a benzene-ring centroid (with 'any substituent') returned 154 hits, none of which have much else in common with I. A crystallographic and computational study of interactions between oxygen lone pairs and aromatic rings (albeit involving carbon-bound oxygen atoms) was presented by Gung et al. (2008).

Synthesis, crystallization and spectroscopic details
In a 250 ml flask (with a nitrogen inlet and a septum) was placed 5 g of 4-fluoro-N-isopropylbenzenamine dissolved in 50 ml of acetonitrile. After cooling to 273 K, 6.7 g of triethylamine and 4.11 g of 2-(methylthio)acetyl chloride were added. The mixture was stirred at room temperature for 5 h. After this, 100 ml of water were added and the mixture was extracted three times, each with 100 ml of methyl tert-butyl ether (MTBE). The combined organic phases were dried over MgSO 4 and the solvent was evaporated under reduced pressure. The crude product, N-(4-fluorophenyl)-N-isopropyl-2-(methylthio)acetamide, was used for the next stage with purification (7.5 g).
To a 250 ml round-bottomed flask (with a nitrogen inlet and a septum) was added 7.5 g of N-(4-fluorophenyl)-N-isopropyl-2-(methylthio)acetamide dissolved in 150 ml of dichloromethane. After cooling to 263-273 K, 13.37 g of metachloroperbenzoic acid in 100 ml dichloromethane was added 514 Geetha et al.  A reaction scheme for the synthesis of I. DCM is dichloromethane, mCPBA is meta-chloroperbenzoic acid.  slowly at the same temperature. The mixture was stirred at room temperature for 5 h. After this, 200 ml of water were added and the organic layer was separated, and washed with 100 ml of 10% sodium bicarbonate twice. The organic phases were dried over MgSO 4 and the solvent was evaporated under reduced pressure. The crude product was purified by chromatography over SiO 2 (hexane:ethyl acetate 9:1 v/v). The title compound was recrystallized from diethyl ether solution in the form of colorless plates. The overall reaction scheme is shown in Fig. 4.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms were found in difference-Fourier maps, but subsequently included in the refinement using riding models, with constrained C-H distances set to 0.95 Å (Csp 2 H), 0.98 Å (RCH 3 ), 0.99 Å (R 2 CH 2 ) and 1.00 Å (R 3 CH). U iso (H) parameters were set to values of either 1.2U eq or 1.5U eq (RCH 3 only) of the attached atom.

N-(4-Fluorophenyl)-2-(methylsulfonyl)-N-(propan-2-yl)acetamide
Crystal data Special details Experimental. The crystal was mounted using polyisobutene oil on the tip of a fine glass fibre, which was fastened in a copper mounting pin with electrical solder. It was placed directly into the cold gas stream of a liquid-nitrogen based cryostat (Hope, 1994;Parkin & Hope, 1998). Diffraction data were collected with the crystal at 90K, which is standard practice in this laboratory for the majority of flash-cooled crystals. Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement progress was checked using Platon (Spek, 2020) and by an R-tensor (Parkin, 2000). The final model was further checked with the IUCr utility checkCIF.